ROOM-TEMPERATURE AMORPHIZATION OF FAYALITE AND HIGH-PRESSURE PROPERTIES OF FE2SIO4 LIQUID

High‐pressure X‐ray diffraction and electron‐microscopy experiments show that fayalite (Fe2SiO4) transforms at around 350 kbar to an amorphous phase that can be quenched down to 1 bar. This room‐ternperature vitrification represents a thermodynamically driven fusion to a glass, as implied by the existence of a maximum above 100 kbar in the metastable extension of the melting curve of fayalite. The diffraction measurements, a thermodynamic analysis of the melting curve of fayalite, and the difference in bulk modulus between fayalite and Fe2SiO4 liquid are consistent with a reversible switch of silicon in the amorphous phase from a high coordination number at pressure down to 4‐fold coordination at 1 bar. Copyright 1990 by the American Geophysical Union.